Composite iron-base metal product

ABSTRACT

A composite iron-base metal product comprising an iron-base metal in which a martensitic structure having a high mechanical strength is formed in a particular portion of the base metal in such a manner that the tensile strength and rupture strength in the direction of orientation of the martensitic structure are improved. The resulting composite product has a tensile strength which approximates the theoretical strength thereof.

United States Patent 119 1 Nemoto et al.

COMPOSITE IRON-BASE METAL PRODUCT Inventors: Tadashi Nemoto, Tokyo;Keiichi Kuniya; Takeo Tamamura, both of Hitachi, all of Japan Assignee:Hitachi, Ltd., Tokyo, Japan Filed: Mar. 29, 1971 Appl. No.: 128,738

Foreign Application Priority Data Mar. 27, 1970 Japan 45-25277 US. Cl148/12.4, 29/l9l.4, 29/196.1,

Int. Cl. lain/90 Field of Search 148/1 1.5, 12, 12.4, 34, 148/3l.5, 39,127, 134, 143, 144; 29/l96.1, 191.4, 197.5, 191.6; 75/135, DIG. 1

References Cited UNITED STATES PATENTS l/l888 Marshall 29/I91.6 X

5/1903 Falk 148/39 7/1951 Kinnear 29/196.1 X 7/1963 Micks 29/l83.59/1965 V0rdahl l48/ll.5 X 11/1965 Allen et al. 29/191.4

[ Sept. 24, 1974 3,314,825 4/1967 Forsyth et al 148/11.5 A

3,419,952 1/1969 Carlson 29/197.5 X

3,450,510 6/1969 Calow 75/D1G. 1

3,466,166 9/1969 Levinstein et al. 75/135 3,489,534 l/l970 Levinstein29/l91.6

3,686,081 8/1972 Butter et al 29/l9l.6 OTHER PUBLICATIONS DMICMemorandum 243, May 1969, Metal-Matrix Composites, pp. l-6.

Blackburn et al., Filament-Matrix Interactions in Metal MatrixComposites, Strengthening Mechanisms, Metals and Ceramic Proceedings ofthe 12th Sagamore Army Materials Conference, Aug. 1965, Syracuse Univ.Press, 1966 pp. 447-475.

Primary ExaminerCharles N. Lovell Attorney, Agent, or Firm-Craig &Antonelli [5 7] ABSTRACT 13 Claims, 10 Drawing Figures PAIENIEUSEPZMHN3.837. 931 m1 '2 Br 4 FIG.Y3

3L ZOEQOZO E m w m ZOO 400 600 TEMPERATURE OF TEMPERlNG ("m INVENTORSTADRSHI NEMOTO, KEHCHI KUNIYA BY AND TAKED TAMAMURA Craig Anlbneui,Stewa t- ATTOR NEIS COMPOSITE IRON-BASE METAL PRODUCT BACKGROUND OF THEINVENTION This invention relates to a new composite metal produce and amethod for producing the same in which grains different from the basemetal are present in clusters therein. More particularly, it relates toa composite iron-base metal product comprising an iron-base metal inwhich a martensitic structure having a high mechanical strength isformed in a particular portion of the base metal whereby the tensilestrength and rupture strength in the direction of orientation of themartensitic structure are improved.

The development of reinforced plastic, in which fiber glass is utilizedto improve defects such as poor strength and poor elasticity of theplastic or synthetic resin, has now reached the stage where it occupiesan established position as an industrial material. However,fiber-reinforced plastics have poor heat resistance, so that the upperthreshold temperature applicable thereto is usually limited to as low asabout 300C.

On the other hand, there has recently been a strong demand for thedevelopment of fiber-reinforced composite metal materials using a metalas a base, and the trend in the industry today is directed toward thisnew product. The aim of developing such fiber-reinforced composite metalmaterials is the obtainment of improved mechanical strength and astriking enhancement of heat resistance, as compared withfiberreinforced plastics (synthetic resins). The key factors in thedevelopment of such fiber-reinforced composite metal materials are theestablishment of techniques of industrially producing metallic fibersand the provision of methods of producing composite metal materialsusing such fibers. It is doubtless that the successful attainment of amanufacturing system, which is industrially acceptable with regard tothe above points, will pave the way for a bright future forfiber-reinforced composite metal materials.

So far, success in connection with the artificial production of whiskersand high strength fine metal fibers has provided a blueprint of a fairprospect of the industrialization of the fibers, and now efforts arebeing made toward establishing a commercially acceptable method forproducing composite metal materials using these metallic fibers.According to the literature published to date concerningfiber-reinforced composite metal materials, many and various attemptshave been made on this subject by utilizing, for example, aninfiltration method, a powder method, a diffusion bonding method or anelectrodeposition method. Most popularly used among these known methodsare the infiltration method, in which a tube filled with fibers isimmersed in a metal bath and molten metal is sucked into the vacuumizedtop portion of the tube, and the diffusion bonding method, whereinmetallic fibers are inserted between the metal plates and are thensubjected to pressure bonding under heating. The fiberreinforcedcomposite metal material thus produced has advantages overfiber-reinforced plastics in that the poor strength and poor elasticityof the base metal are sufficiently covered up and overcome by the fibersand a far higher heat resistance than that of fiber-reinforced plasticmaterial is obtained.

It is, therefore, a natural consequence that the development of suchfiber-reinforced composite metal materials will represent a breakthroughin a new field which is of a completely different nature from theconventional property-improving methods based on the alloying of metals.in this connection. it is also inevitable that some difficult problemsare encountered. For example, a fiber-reinforced composite metalmaterial is subject to restriction by the differences in adhesion andcoefficient of thermal expansion between the base metal and the fibers,so that practical uses thereof are confined to the scope of specificcombinations. Also, the property of the resultant material cannot bebetter than what may result from a combination of the properties of therespective components. The fact should also not be ignored that theartificially produced whiskers or high strength fine fibers areextremely expensive.

These facts dictate that success in varying the properties of metallicfibers in combinations of base metal and fibers will result in anappreciably widened scope of application of the material. Also, if amethod involving no need of using expensively produced whiskers or highstrength fine fibers should be devised, it will open up a way fordeveloping a completely new type of composite metal material which isbeyond the scope of fiberreinforced composite metal materials.

The present invention is intended to meet all of these factors, and,therefore, the primary object of this invention is to provide a novelcomposite iron-base metal product in which the properties of theelements included in the base metal are varied.

Another object of the invention is to provide a method for producingsuch composite metal products.

tion and claims, taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION Essentially, the composite iron-base metalproducts of the present invention can be obtained by giving a certaindirectionality to the grains produced by the reaction between the basemetal and the elements reactable therewith.

The method of producing such composite metal products according to thepresent invention comprises, essentially, the steps of incorporating inan iron-base metal the elements reactable therewith in such a mannerthat they are kept safe from the influence of oxygen,- and reacting themby a heat treatment at a temperature lower than the melting point of thebase metal.

Although iron and steel materials have the broadest scope of utilizationin present day industrial circles, few experimental attempts have beenconducted to date for improving fiber-reinforced composite metalmaterials because of the failure to find out fibers which areeffectively utilizable for the reinforcement of iron and steel.Therefore, the strengthening of such materials has heretofore reliedupon the selection of alloying elements and of heat treatmentconditions. The application of the present invention to iron-typecomposite metal products is characterized by employing the concept of atransformation of the structure. It is a typical embodiment of thepresent invention to form a martensite structure with a certaindirectionality in an iron base having high strength, thereby maintainingthe strength of the product with the presence of martensite and tocompensate for the brittleness of martensite with the tenacious natureof base iron.

In order to embody this principle and concept into the fiber-reinforcedcomposite metal materials which are now being developed, a firstconsideration is paid to the modification of brittle martensite into theform of a fiber. To this end, finely pulverized pieces or powder ofcarbon, foil, paper or the like may be utilized in the presentinvention. The fibers employed in this connection do not necessarilyhave to be whiskers or strong fine metal fibers. The fibers employed maybe weak in and of themselves.

The strength of martensite produced by the reaction of iron and carbonis not as low as that of ordinary alloyed steel, but actuallyapproximates the intrinsic theoretical value. From this fact, it will beunderstood that the elements worked into a powder or foil can beeffectively utilized in a manner to be more particularly describedhereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 is a graph showing the relationship between the tensile strengthand carbon content of ordinary martensitic alloyed steel;

FIG. 2 is a graph showing the effect of carbon content on 0.6 percentproof stress of an iron-nickelcarbon alloyed steel;

FIG. 3 is a graph showing the relationship between tensile strength andelongation percentage and carbon content of martensitic carbon steel,and;

FIGS. 4, 5, 6, 7, 8, 9 and 10 are perspective views illustrating variousembodiments of the composite metal products of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows thetensile strength, in comparison with carbon content, of the martensitestructure of alloyed steel for general use when it is tempered at 200C.Since these alloyed steel materials were produced by ignoring theirelasticity, they have an extremely small elongation percentage. For thesake of comparison, similar data are also given for carbon steel, butthese data are the presumed values which are considered to beintrinsically possessed by carbon steel. It will be understood from thisfigure that the tensile strength of martensite is improvedproportionally to an increase of the carbon content.

FIG. 2 shows the results of experiments conducted with theiron-nickel-carbon alloyed steel as an example to show the proof stressof martensite steel. The 0.6 percent proof stress [the quotient obtainedby dividing the load (kg), at which a permanent elongation of 0.6percent takes place, by the original sectional area (mm of the parallelpart in a tensile test or compression test] is given on the ordinate,and the carbon and nickel contents are shown on the abscissae.

In FIG. 2, curve (I) shows the compression proof stress observed in acompression test after an aging treatment for three hours at C., andcurve (2) shows the tensile proof stress observed in a tensile test withno age treatment being conducted. It is to be noted from FIG. 2 that thetensile strength is steadily increased. until the carbon content reachesthe 0.6 percent level. It has thus been found that the strengthcharacteristic of martensite is improved proportionally to an increasein the carbon content until the latter reaches the 0.5 to 0.6 percentlevel, but above that level, no such improvement is observed.

This fact is evidently attested to by FIG. 3, wherein the tensilestrength and elongation percentage of the three carbon steel martensitetest pieces having different carbon contents from each other are shownin relation to tempering temperature. In FIG. 3, curves (3) and (3a)represent steel containing 0.34 percent of carbon and being oil-quenchedstarting from 850C curves (4) and (4a) represent steel containing 0.65percent of carbon and being oil-quenched starting from 850C, and curves(5) and (50) represent steel containing 0.99 percent of carbon and beingwaterquenched from 750C. Curves (3), (4) and (5) show tensile strength,while curves (3a), (4a) and (5a) show elongation percentage.

The results of FIG. 3 reveal that the tensile strength of carbon steelis rather low when the carbon content is up to about 1 percent. However,in view of the fact that, intrinsically, strength and elongation arecontradictory factors, a reasonable conclusion is that the true tensilestrength of steel containing 0.99 percent carbon, which has the lowestelongation percentage, should be the highest among the curves (3), (4)and (5). Actually, however, it only exhibits a low tensile strength suchas represented in the graph. This is attributable to the fact that toohigh of an increase of the carbon content invites premature rupturephenomenon, which makes it impossible to obtain a true tensile strength.

Owing to these reasons. in the field of iron alloys, it has not beenpossible to fully utilize the intrinsic strength of martensitecontaining a large amount of carbon, and even maraging steel, which isrepresentative of high-strength martensite steel, had a tensile strengthas low as below 200 kglmm However, in the composite metal productsaccording to the present invention, even if local rupture would becaused due to brittleness of the martensite structure produced byreaction with the iron base, the destructive energy is absorbed by thetenacious iron base, so that such rupture does not extend over theentire composite metal material but is forced to advance in astepby-step manner. It is thus possible to fully utilize the excellentstrength characteristics of martensite, which contains carbon inabundance.

The present invention also overthrows the conventional conception offiber-reinforced composite metal materials, which dictates that it isnecessary to previously prepare the martensite fibers, which are verydifficult to produce, since it is contemplated to utilize forreinforcement the particles of martensite produced by reaction betweenthe iron base and carbon introduced therein. Hence, the technicaldifficulties in this respect are removed. Furthermore, the utilizationof the reaction between the iron base and carbon brings about theadvantage that the element incorporated may be, in itself, weak fibersor may be in the form of a powder or foil. It should, however, be keptin mind that, in the case of using a powder or foil, the martensitegrains must be arranged with directionality.

Thus, one of the important features of the present invention is that theelement incorporated in the metal base becomes a component of the basethrough reaction therewith and, as a result, a metal product presentingthe same structure as that of an alloy product is obtained.

In a composite metal material where the fibers are arranged continuouslyin one direction, the average tensile strength 8 of this material, whena tensile force is acting in the fiber direction, is expressed by thefollowing formula:

0 f I m m SIVI m( VI), wherein 6, stands for the tensile strength of thefiber, 8, represents the inherent tensile strength of the base metal,8', is the stress of the base metal in regard to the rupture strain ofthe composite metal material, and V; and V,,, represent the volumeratios of fiber and base metal, respectively.

Now, by way of example, martensite grains having a 1 percent carboncontent are produced in a ferrite base such that the amount ofmartensite takes 70 percent (in one embodiment) and 50 percent (inanother embodiment) of the entire composite metal material. In thiscase, as mentioned above, when the carbon content in carbon steelmartensite reaches a 1 percent level, a premature rupture phenomenon iscaused and, therefore, a true tensile strength is not exhibited.However, as estimated from the tensile strength of martensite of lowcarbon content (0.1 to 0.6 percent), it may be considered that thetensile strength of martensite containing 1 percent carbon must be about320 kg/mm when it is tempered at 200C. Likewise, the tensile strength offerrite is estimated to be about 31 kglmm Also, the stress 6', of thebase metal, that is, ferrite in this case, in rupture strain of thecomposite metal material may be estimated to be about 14 to 17 kg/mmIntroducing these estimated values into the above formula, the followingresults are obtained:

In case the volume ratio of the martensite structure is 0.7,

8,. 320 X 0.7 X 0.3 228.5 kglmm In case the volume ratio of themartensite structure is 0.5,

8, 320 X 0.5 +15 X 0.5 167.5 kglmm These results indicate that even ifthe base iron is of low strength, the martensite structure willcompensate for it and a high strength product can be obtained. As to theelastic property, such as elongation or contraction, this is wellsupplemented by the base iron, so that the product of such high strengthis also provided with excellent elasticity and tenacity.

It will be understood from the examples described hereinbelow thattensile strength calculated in this manner substantially agrees with theactually measured tensile strength of the composite metal product and,thus, the intrinsic tensile strength of martensite is displayed in sucha case.

Now, the essential means employed for producing the composite metalproducts according to the present invention will be described in detail.

Referring first to FIG. 4, which shows an embodiment of the presentinvention, it will be seen that grooves 2 are formed in a metal base 1and that elements 3 reactable with the base metal are disposed in saidgrooves in a manner as shown in FIG. 5. Formation of grooves 2 in themetal base 1 may be accomplished by using any suitable conventionalmechanical method, such as, for example, marking-off. It is alsopossible to employ photo-etching, which is popularly used insemiconductor devices. It is preferable not to make the depth of thegrooves 2 too large. This is because if the groove depth is too large,the grooves will not vanish and will remain as voids even if subjectedto rolling after or during the manufacture of the composite metalproducts. The presence of such voids causes a decline of strength.

The grooves are provided in sufficient number to satisfy the requiredvolume ratio of the elements disposed therein. It is to be noted that ifthese grooves are pro vided in regular order in one direction alone, avariation of characteristic by reaction between the metal base and theelements appears conspicuously only in that direction, withsubstantially no effect appearing in the direction which crosses theabove-said direction, so that, if necessary, similar grooves can beprovided in the crossing direction also.

After providing a required number of grooves in the metal base in theabove-described manner, the elements 3 reactable with the base metal arethen placed in the grooves. It should be noted that if the elements thusplaced in position are directly subjected to heating in an oxygenatmosphere, they will be oxidized to produce an oxide, such as, forexample, CO or CD so that the desired results will not be obtained. Itis therefore necessary to conduct a heating treatment after sealing thegrooves 2 so as to keep them free from the influence of oxygen. One ofthe convenient measures for carrying out this treatment is to place anew metal base 1A in close contact with the surface of the metal base 1where the grooves 2 are formed, as shown in FIG. 4. For industrial use,it is necessary to laminate the metal bases in many layers to produceone article, so that this measure proves extremely effective. Even inthe case where the metal bases are laminated in many layers, it isdesirable to seal the grooves at the end faces by means of welding orsoldering.

In another embodiment, as shown in FIG. 6, holes 4 are provided in themetal base 11 and the element 3 reactable with the base metal are placedin said holes. These holes may be formed easily by the use of a drill orother like means. Since it is difficult to form small holes from thebeginning, it is recommended to first form comparatively large holes andthen to stretch the metal base 11 by rolling to thereby make the holessmaller. It is also practical to arrange, with a certain directionality,the elements 3 reactable with the base metal directly on the surface ofa flat plate-shaped metal base 1, as shown in FIG. 7, and to let themreact under this state. In this case, a prevention against oxidation ofthe elements 3 may be achieved by using new metal bases 1A, 1B and 11Cin the same manner as in the case where the grooves 2 are provided inthe metal bases are to be combined together integrally, they are firstsuitably bundled together as shown in the figure, with the contactingfaces being welded together, and are then subjected to a rollingoperation to remove the grooves into the form of a plate.

In the case of including the reactable elements in the metal base, it isalso possible to include other kinds of elements along with thementioned reactable elements. An example of such a situation isillustrated in FIG. 10, where the elements 3 and 3A are disposed in thegrooves 2 formed in the metal base 1. Both elements 3 and 3A may beelements which react with the base metal or with each other. Of course,the element 3A may be an element which does not react either with thebase metal or with the element 3. in this case, high strength finefibers are preferred.

In the case that different kinds of elements are arranged with eachother as mentioned above, if the elements 3A are capable of reactingwith base metal 1 or with the elements 3, it is possible to controlexcess diffusion of the elements 3 into the metal base.

In the case of having martensite particles existing in an iron base, aniron-carbon alloy base is previously prepared and pure iron isdistrubuted therein with a certain directionality, the structure thenbeing subjected to heat treatment. The amount of included pure iron,which is reacted with carbon in the base, is extremely small, so that itis reduced into ferrite while the base metal is turned into martensite.

When pure iron is distributed with a certain directionality in, forexample, an 18 percent chromium-8 percent nickel steel base having astable austenite structure, and this base is subjected to heattreatment, the nickel and chromium in the base at the part in thevicinity of pure iron are diluted and turned into a martensiticstructure area, while the part remote from pure iron remains asaustenite.

The proper range of heat treatment temperature and heating time may varyaccording to the thickness and composition of the metal base and theamount of elements included in the base, but, basically, the purpose canbe obtained if such temperature is above the lower threshold temperatureat which the base metal and the elements are reacted. For instance, inthe case of generating martensite containing 1 percent carbon byreacting pure iron and carbon, the heat treatment is preferablyconducted within the temperature range of from 770 to 850C. A rise ofthe heat treatment temperature promotes diffusion of the elements intothe base, so that when it is desired to further raise the heat treatmenttemperature, the heating time can be shortened correspondingly.

EXAMPLES OF THE INVENTION The following examples are given merely asillustrative of the present invention and are not to be considered aslimiting.

EXAMPLE 1 Grooves about 0.1 mm. in depth and width were formed atintervals of about 2 mm., by marking-off, on the surface of a pure ironplate having a thickness of mm., a width of 100 mm. and a length of 200mm. Carbon fibers were then distributed therein. The carbon fibers usedwere not high strength fine fibers, but weak fibers in and ofthemselves, and they were arranged continuously with no breaksthroughout. The amount of the carbon fibers was selected such thatmartensite containing 1 percent carbon will be present in an amount of50 percent by volume ratio.

Then, a metal plate having the same size as said pure iron plate wasplaced on the surface of the latter where the grooves were formed, andafter sealing the periphery by tungsten inert gas welding (referred toherein as TlG welding), the assembly was subjected to hot rolling. Thehot rolling procedure flattened the plate assembly to a thickness ofabout 5 mm. After rolling the assembly was heated at 800C. to causereaction between the pure iron base and the carbon fibers and wasmaintained at that temperature for 30 minutes and thereafter immersed inwater to effect cooling. Then, the assembly was further subjected to atempering treatment at 200C. to improve the toughness of the pure ironplate and the generated martensite.

Thereafter, specimens for a tensile strength test were collected fromthe obtained composite metal product and were subjected to tests todetermine their tensile strength and elongation percentage. Thespecimens were collected in such a way as to allow a determination ofthe strength in the direction where the martensite grains are arrangedcontinuously. The tensile strength was 150 kg/mm and the elongationpercentage was l5 percent.

These results agree well with the calculated values obtained from theformula for calculating the average tensile strength of a compositemetal material having fibers arranged continuously in one direction inthe case where a tensile force is applied therein in the direction ofthe fibers.

EXAMPLE 2 Holes having a diameter of 2 mm. were formed by a drillcentrally (of the thicknesswise direction) in a pure iron plate having athickness of 10 mm., a width of 100 mm. and a length of 200 mm. Twentyof such holes were formed equidistantly along the longitudinal length ofthe plate.

Then, the same carbon fibers as used in Example 1 were inserted intothese holes, and the plate was then subjected to cold rolling in anargon atmosphere to flatten the plate to a thickness of about 7 mm. Theamount of carbon fibers was adjusted such that martensite containing 1percent carbon will be present in an amount of percent by volume ratio.Then, three pieces of similar composite metal plates produced in thesame manner were placed thereon in layers, and after sealing theperiphery by TlG welding, the entire assembly was subjected to hotrolling in an argon atmosphere to reduce the total thickness to 5 mm.The resultant composite metal product was heated at 800C. for 30 minutesand then cooled in water in the same manner as in Example 1. Thereafter,the product was further sub jected to a tempering treatment at 200C. Thetensile strength and elongation percentage in the longitudinal directionof the product were 205 kg/mm and 14 percent, respectively.

EXAMPLE 3 Carbon fibers were arranged in 20 rows equidistantly on a pureiron plate having a thickness of 0.2 mm., a width of mm. and a length of200 mm. Then, another pure iron plate of the same dimension was placedon said rows of carbon fibers, and on this position were arranged anadditional 20 rows of carbon fibers, on

which another such plate was placed. in this manner, a lamination of 30layers in all was formed (each layer consisting of a pure iron plate and20 rows of carbon fibers lodged thereon). Finally, the surface of thetopmost rows of carbon fibers was covered with a pure iron plate, andthe assembly was subjected to hot rolling in a vacuum atmosphere toreduce the total thickness thereof to 2 mm.

Thereafter, the assembly was subjected to quenching and temperingtreatments under the same conditions as in Examples 1 and 2. The amountof carbon fibers becomes adjusted such that martensite containing 1percent carbon will occupy 70 percent by volume of the entire structure.

The resultant composite metal product has a tensile strength of 208kg/mm and an elongation percentage of 15 percent.

EXAMPLE 4 A cloth of carbon fibers woven in lattice shape (with aspacing of 5 mm.) was placed on the surface of a pure iron base having athickness of 3 mm., a width of 100 mm. and a length of 200 mm., tothereby form a unitary structure, and the resulting structures wereplaced one on the other in layers. Finally, the topmost surface wascovered with a pure iron plate, and the entire assembly was subjected tohot rolling in an argon atmosphere to make a total thickness of 8 mm.

The amount of the carbon cloth becomes adjusted such that martensitecontaining 1 percent carbon takes 50 percent by volume of the entirestructure. Thereafter, quenching and tempering treatments starting at800C. were conducted in the same manner as in the previous examples. A

The tensile test results showed that the obtained product had a tensilestrength of 120 kg/mm and an elongation percentage of 14 percent.

EXAMPLE 5 Japanese paper was placed on the surface of a pure iron platehaving a thickness of 3 mm., a width of 100 mm. and a length of 200 mm.,and 5 groups of this combination were laminated in layers, with thetopmost surface being covered with a pure iron plate. Then, the entireassembly was subjected to pressure welding under heating in an argonatmosphere to reduce the total thickness therof to 7 mm. Consideringthat about 50 percent of the paper contributes as carbon, the amount ofpaper was adjusted such that martensite containing 1 percent carbon willexist in an amount of 50 percent by volume ratio. After heating at 800C.for 30 minutes, the assembly was subjected to water quenching andtempering treatments.

The obtained product had a tensile strength of 125 kg/mm and anelongation percentage of 14 percent.

EXAMPLE 6 Then, seven pieces of the resulting composite metaltubes wereassembled into a bundle, with the contacting faces being welded togetherby TlG welding, and then the bundle was subjected to hot rolling toflatten it into the form of a plate having a total thickness of about 1mm.

The composite metal product thus obtained had a tensile strength of l5lkg/mm and an elongation percentage of 14.4 percent.

EXAMPLE 7 Grooves having a depth and width of about 0.1 mm. were formed,by marking-off, at intervals of about 2 mm. along the longitudinallength of a base plate formed from an iron alloy containing 5.4 percentof nickel-having a thickness of 5 mm., a width of 100 mm. and a lengthof 200 mm. Then, carbon fibers were placed in the grooves. The amount ofcarbon fibers was such that martensite including 1 percent carbon wouldbe obtained in an amount of 70 percent by volume ratio. Then, a plate ofthe same composition and same dimension as the base plate was disposedon the surface of the latter where the grooves were formed, and afterperforming TIG welding around the periphery, the assembly was subjectedto hot rolling. The plate thickness was lessened to 5 mm. by rolling.Thereafter, the structure was heated at 850C, maintained at thattemperature for 30 minutes, immersed in water to effect cooling, andthen further subjected to a tempering treatment at 200C.

The resulting composite metal product had a tensile strength of about215 kg/mm and an elongation percentage of l 1.6 percent.

As can be seen from the foregoing examples, the composite metal materialprepared by distributing carbon in an iron base and reacting the same byheat treatment such that martensite grains exist therein with a certaindirectionality has a higher tensile strength and toughness than ordinarycarbon steel or alloyed steel, since the strength characteristic isprovided by martensite, while toughness is provided by the iron base. It

i is also apparent that these effects are not obtained by the simpleinclusion of carbon fibers in the iron base; rather, the characterizingproperties stem from the generation of grains having differentcharacteristics, that is, martensite grains, by reaction between suchcarbon fibers and the iron base.

The modes of embodiments of the present invention are exemplified asfollows:

1. A composite metal product comprising a metal base and the elementsreactable therewith, said elements being present in continuation in agiven direction and reacted with the base metal adjacent thereto by heattreatment at a temperature lower than the melting point thereof tothereby form the grains.

2. A composite metal product comprising a metal base and a plurality ofdifferent kinds of elements, at least one of which is reactable with thebase metal, said elements being present in continuation in a givendirection and being reacted with the base metal adjacent thereto by heattreatment at a temperature lower than the melting point thereof tothereby form more than one grain cluster.

3. A composite metal product comprising a metal base and elementsreactable therewith, said elements being enclosed in the grooves are insaid metal base condition free from the influence of oxygen to therebyform a cluster of grains.

4. A composite metal product comprising a metal base and the elementsreactable therewith, said elements being enclosed in holes provided insaid metal base with a certain directionality and being reacted with thebase metal adjacent thereto by heat treatment under a condition freefrom the influence of oxygen to thereby form a cluster of grains 5. Acomposite metal product comprising a lamination of plural metal basesand elements reactable therewith, said elements being laminatedalternately with said metal bases in layers and being reacted with thebase metal adjacent thereto by heat treatment under a condition freefrom the influence of oxygen to thereby form a cluster of grains.

6. A method of producing a composite metal product comprising the stepsof placing in a metal base the elements reactable therewith in acontinuous arrangement in a certain given direction and, after sealingsaid elements so as to remain free from the influence of oxygen,reacting said base metal and elements by heat treatment at a temperaturelower than the melting point thereof.

7. A method of producing a composite metal product comprising the stepsof placing in a metal base a plurality of different kinds of elements,at least one of which is reactable with said base metal, in a continuousarrangement in a certain given direction and, after sealing saidelements so as to remain free from the influence of oxygen, reactingsaid base metal and elements by heat treatment at a temperature lowerthan the melting point therof.

8. A method of producing a composite metal product comprising the stepsof placing in grooves provided in a metal base with a certaindirectionality the elements reactable with said metal base and, aftersealing said elements so as to remain free from the influence of oxygen,reacting said base metal and elements by heat treatment at a temperaturelower than the melting point thereof.

9. A method of producing a composite metal product comprising the stepsof placing in holes provided in a metal base with a certaindirectionality the elements reactable with saidmetal base and, aftersealing said holes so as to keep the elements free from the influence ofoxygen, reacting said base metal and elements by heat treatment at atemperature lower than the melting point thereof.

10. A method of producing a composite metal product comprising the stepsof placing on the surface of a metal base the elements reactabletherewith in a continuous arrangement in a certain given direction,laminating said metal bases and elements alternately in many layers, andafter sealing said elements to keep them free from the influence ofoxygen, reacting said elements with the base metal by heat treatment ata temperature lower than the melting point thereof.

Although in the above description, carbon has been exemplified as beingutilized with the composite ironbase metal products for improving ormodifying the characteristics of the iron-base metal, it has been foundthat elements having a mutual solid solubility with the iron-base metaland being capable of producing the y a transformation when the iron-basemetal is subjected to cooling can be suitably employed.

As such elements, there may be mentioned W, Cr, Si, V, Mo, Ti, Be, Cu,P, S, Ni and various mixtures thereof. Of these elements, P and S may beused for improving the workability of the iron-base metal. and W, Cr,Si, V, Mo, Nb and Ti may be used for improving the mechanicalcharacteristics of the iron-base metal. For example, several pipes madeof Fe 5% Ni, wherein the holes are filled with a powder of W, aretightly bundled and are twisted to make the pipes into an assembly,followed by heat treatment under such a condition that the W atoms arediffused into the iron-base metal. instead of the W powder, fine wiresor fibers of W or Mo, which are widely used in the field of conventionalcomposite materials, can also be employed.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included herein.

We claim:

1. A method for producing a composite metal product comprising the stepsof:

orienting at least one elongated carbon element in an metal baseselected from group consisting of iron and iron alloys such that saidelement extends in at least one predetermined direction with respect tothe metal base;

sealing said element within said metal base such that said element isprotected from an oxidizing atmosphere; heating the resulting compositeof metal base and oriented element at a temperature of from about 770Cto about 850C for a period of time determined such that substantiallyall of the carbon of said element reacts with the iron in said metalbase which is substantially in the region adjacent said orientedelement, thereby forming an oriented portion in said metal base having a'y structure; and

quenching the thus heated resulting composite to cause said orientedportion to have a martensitic structure said structure being differentfrom that of the metal base.

2. The method of claim 1, wherein a plurality of said elongated carbonelements are oriented in said metal base, and a plurality of orientedportions having the martensitic structure are formed in said resultingcomposite during said quenching.

3. The method of claim 1, further comprising the step of tempering saidresulting composite at a temperature of 200C following said quenchingstep.

4. The method of claim 2, wherein the metal base is formed of a sheet,and the step of orienting includes forming a plurality of grooves insaid predetermined direction on one surface of said sheet and disposingsaid plurality of elongated elements into said grooves.

5. The method of claim 4, wherein said step of sealing includeslaminating a second metal sheet of material substantially the same assaid metal base on said one surface and sealing edges of the laminatedsheets by welding.

6. The method of claim 5, further comprising, after the step of sealing,hot rolling said laminated sheets to compress said laminated sheetswhereby said grooves are completely filled by said elongated elements.

7. The method of claim 6, wherein said laminated sheets are heated at atemperature of 800C for a period of 30 minutes, and quenched in water.

8. The method of claim 5, further comprising the steps of providing aplurality of said laminated sheets in a stack, laminating said pluralityof sheets to one another, and hot rolling said laminated stack todecrease the thickness of said laminated stack prior to the step ofreacting.

9. The method of claim 8, wherein said laminated stack is heated at atemperature of 800C for a period of 30 minutes, and quenched in water.

10. The method of claim 2, wherein said metal base is formed of a plate,and the step of orienting includes drilling a plurality of holes in acentral thickness direction of said plate and filling said holes withsaid plurality of elongated elements.

11. The method of claim 10, wherein the step of sealing includes coldrolling said filled plate to compress the thickness of said plate,thereby completely filling said holes by said elongated elements andsealing the ends of said plate having holes formed therein by welding.

12. The method of claim 11, wherein said filled plate is heated at atemperature of 800C for a period of 30 minutes, and quenched in water.

13. The method of claim 1, wherein said carbon elements are selectedfrom a material consisting of carbon fibers, elements formed of carbonpowder, carbon cloth, carbon foils and carbon paper,

2. The method of claim 1, wherein a plurality of said elongated carbonelements are oriented in said metal base, and a plurality of orientedportions having the martensitic structure are formed in said resultingcomposite during said quenching.
 3. The method of claim 1, furthercomprising the step of tempering said resulting composite at atemperature of 200*C following said quenching step.
 4. The method ofclaim 2, wherein the metal base is formed of a sheet, and the step oforienting includes forming a plurality of grooves in said predetermineddirection on one surface of said sheet and disposing said plurality ofelongated elements into said grooves.
 5. The method of claim 4, whereinsaid step of sealing includes laminating a second metal sheet ofmaterial substantially the same as said metal base on said one surfaceand sealing edges of the laminated sheets by welding.
 6. The method ofclaim 5, further comprising, after the step of sealing, hot rolling saidlaminated sheets to compress said laminated sheets whereby said groovesare completely filled by said elongated elements.
 7. The method of claim6, wherein said laminated sheets are heated at a temperature of 800*Cfor a period of 30 minutes, and quenched in water.
 8. The method ofclaim 5, further comprising the steps of providing a plurality of saidlaminated sheets in a stack, laminating said plurality of sheets to oneanother, and hot rolling said laminated stack to decrease the thicknessof said laminated stack prior to the step of reacting.
 9. The method ofclaim 8, wherein said laminated stack is heated at a temperature of800*C for a period of 30 minutes, and quenched in water.
 10. The methodof claim 2, wherein said metal base is formed of a plate, and the stepof orienting includes drilling a plurality of holes in a centralthickness direction of said plate and filling said holes with saidplurality of elongated elements.
 11. The method of claim 10, wherein thestep of sealing includes cold rolling said filled plate to compress thethickness of said plate, thereby completely filling said holes by saidelongated elements and sealing the ends of said plate having holesformed therein by welding.
 12. The method of claim 11, wherein saidfilled plate is heated at a temperature of 800*C for a period of 30minutes, and quenched in water.
 13. The Method of claim 1, wherein saidcarbon elements are selected from a material consisting of carbonfibers, elements formed of carbon powder, carbon cloth, carbon foils andcarbon paper.